1. Field of the Invention
The present invention relates to an information processing system having backup/recovery facilities, more particularly relates to a backup/recovery technique of data introduced in a main storage in that system.
In information processing systems, generally use is made of the technique of backing up data by loading data of a direct access storage device (DASD), for example, a magnetic disk unit, one type of external storage unit, in another external storage unit, such as a magnetic tape unit, to prepare against a fault or the like and recovering data by reading out the data from that other external storage unit when a fault occurs in the DASD.
So as to carry out such a backup/recovery, there is a method in which the data is physically read out and transferred from the DASD in certain units of volume in the order of the recordation and then is loaded in an external magnetic tape unit etc. In this method, however, the data (including a program) read out from the DASD to a main storage or a system storage unit (memory for expanding the main storage, abbreviated as SSU) is processed at a central processing unit (CPU), and therefore it is not the same as the original data. For this reason, so as to reliably perform the backup/recovery of the data, it is necessary to fetch also the contents loaded in the main storage (or SSU) into the magnetic tape unit etc.
2. Description of the Related Art
Conventionally, where backup/recovery is carried out, as will be explained later with reference to the drawings, to back up the data of the DASD after the data of the main storage is reflected in it, it is necessary to write the data in the main storage back to the DASD, so a long time is taken for performing the logical processing, for example, converting the address in the main storage to an address in the DASD. Further, after the data is written in the DASD, the data is further written in the magnetic tape unit etc. via a buffer of the main storage, and therefore there arises a problem in that the processing load for the backup was large and a long time was taken. Also, even when recovering the contents after backup, after the data is loaded in the DASD from that magnetic tape unit etc., it is necessary to further restore the state before the fault occurred by writing the same data as that immediately before the related backup is carried out into the main storage from the DASD, and therefore a problem of a long processing time occurred.